Applied Microscopy最新文献

This study investigated the gilding microstructures and manufacturing techniques of a fifth-century Silla horse-harness fitting excavated from the grave-goods compartment of Hwangnam-dong Tomb No. 120-2 in Gyeongju, Korea. The specimen comprised two structural components: a gilded copper plate and a connecting iron rivet wrapped in gilded silver sheet. A single polished cross section prepared from the artifact was examined by stereomicroscopy, reflected-light metallurgical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Residual Hg in the gilded regions of both components supports the use of mercury-amalgam gilding. Gilding-related microstructures survived on both faces and at the bent ends of the silver sheet, consistent with gilding before wrapping the rivet. EDS analysis detected Au and Hg in the amalgam regions. High-magnification imaging revealed granular remnants at both ends of the rivet that may represent Au–Hg amalgam residues associated with incomplete finishing. Local gilding thicknesses at two locations on the copper plate were 1.33 ± 0.53 μm and 1.01 ± 0.23 μm, whereas the bright gilded regions on opposite faces of the silver sheet measured 3.69 ± 1.04 μm and 3.52 ± 0.63 μm. These measurements document local thickness differences between gilded regions on copper and silver substrates within one cross section. Together, the terminal granular remnants and substrate-associated differences in local gilding thickness provide evidence for reconstructing the gilding sequence and finishing practices employed in fifth-century Silla metalworking.

Three-dimensional (3D) integrated one-selector one-resistor (1S1R) cross-point arrays are emerging as a leading next-generation memory technology. Achieving both nonvolatile memory switching and volatile threshold switching within a single material system offers tremendous potential for simplifying fabrication. This study demonstrates that the memory and threshold switching behavior of germanium-telluride (Ge_xTe_1-x) devices can be precisely tuned by controlling their atomic ratio. In the Te-deficient Ge_xTe_1-x system, the device exhibits nonvolatile memory switching with fast operating speed. Conversely, the Te-rich system functions as an excellent bidirectional selector for high-density memory applications, exhibiting high selectivity (> 10⁴) and a short delay time (< 55 ns). Material analyses using X-ray photoelectron spectroscopy and Raman spectroscopy reveal that these distinct electrical behaviors are driven by composition-dependent changes in the atomic structure. Furthermore, the fully integrated 1S1R stack demonstrates robust SET/RESET switching characteristics, maintaining a stable memory window of 0.2 V and an on/off current ratio exceeding two orders of magnitude (~ 1.12 × 10²). Notably, this integrated configuration provides superior operational reliability and enhanced endurance (~ 8 × 10⁶ cycles) compared to standalone phase-change memory devices. By elucidating these underlying mechanisms, this work reduces the fabrication complexity of stackable devices and opens up wide-ranging applications for unified memory and selector systems.

Anatase titanium dioxide (TiO₂) is widely recognized for its superior photocatalytic capabilities due to its indirect band gap, low cost, and high chemical stability compared to other oxide semiconductors. Despite its advantages, TiO₂ still suffers from intrinsic limitations, particularly rapid charge carrier recombination. To overcome these limitations, extensive research has focused on tailoring the surface structure of TiO₂, particularly through morphology engineering that optimizes facet exposure and improves reactivity. In terms of photocatalysis, two surfaces can be mainly considered in anatase TiO₂: (001) surface with notably high reactivity and (101) surface with lower reactivity; and thus the higher photocatalytic activity requires a higher proportion of the (001) surface, which contradicts to fact that the (001) and (101) surfaces have the surface energies of 0.90 J/m² and 0.44 J/m², respectively. We attempt Sn-doping to reduce the surface energy disparity and then stabilize the (001) surface. Our results demonstrate that Sn incorporation during growth stabilizes the (001) facet and promotes the formation of a (001)/(101) facet heterojunction. CL measurements further show suppressed radiative recombination relative to an undoped TiO₂ thin film. We provide insights into the approach for achieving facet-selective surface stabilization through Sn incorporation.

Optoelectronic characterization of local bandgap, dielectric response, and plasmon at the nanometer scale has become increasingly important for understanding and optimizing modern electronic, optoelectronic, and quantum materials. Conventional optical techniques generally provide spatially averaged information and are therefore limited in their ability to resolve localized electronic variations arising from defects, interfaces, strain fields, and quantum confinement. To overcome these limits, monochromated scanning transmission electron microscopy–valence electron energy loss spectroscopy (STEM-VEELS) has evolved from a qualitative low-loss spectroscopy technique into a quantitative nanoscale bandgap metrology platform. By analyzing low-loss inelastic scattering signals with a sub-nanometer electron probe and sub-100 meV energy resolution, STEM-VEELS enables the direct investigation of bandgap onsets, local density of states (LDOS), and interband transitions at the nanoscale, although the effective spatial resolution of these measurements can be substantially broader than the probe size because of inelastic-scattering delocalization.

This review summarizes the fundamental principles and recent advances in monochromated STEM-VEELS for local bandgap measurement. Particular emphasis is placed on the physical origin of low-loss excitations, addressing critical challenges such as momentum transfer and spatial delocalization. Practical experimental strategies for rigorous zero-loss peak (ZLP) subtraction and bandgap onset determination are systematically discussed. Furthermore, major analytical artifacts—such as Cherenkov radiation, guided optical modes, and beam-induced damage—are critically reviewed alongside state-of-the-art mitigation strategies.

Recent developments in off-axis and Bessel-aperture STEM-VEELS geometries, machine-learning-assisted spectral analysis, automated onset extraction, and uncertainty-aware bandgap mapping are highlighted. Representative applications involving quantum dots, wide-bandgap oxides, heterointerfaces, and two-dimensional materials demonstrate the unparalleled capability of STEM-VEELS to resolve spatially varying electronic structures. Finally, future perspectives, including operando spectroscopy, ultrafast VEELS, artificial intelligence-driven analysis, and SEM-REELS, are discussed, providing a robust framework for standardization and quantitative nanoscale bandgap metrology.

Focused ion beam–scanning electron microscopy (FIB–SEM) was used to investigate the effects of acceleration voltage, beam current, and cryogenic conditions on the cross-sectional preparation of proton exchange membrane fuel cell (PEMFC) cathode catalyst layers. Milling at 30 kV and 0.26 nA effectively minimized curtaining artifacts and produced an apparent cross-sectional pore morphology similar to that obtained by cryogenic milling, indicating that optimized room-temperature milling can provide cross sections suitable for consistent two-dimensional (2D) pore-area analysis under the conditions examined.

Representative FIB–SEM cross-sectional images of PEMFC cathode catalyst layers prepared under different FIB milling conditions: (a–c) 5 kV at room temperature, (d–f) 30 kV at room temperature, and (g–i) 30 kV under cryogenic conditions (− 150 °C). The indicated voltage and current values represent the FIB acceleration voltage and ion beam current used for milling, respectively. The red dashed box in (f) highlights the optimized room-temperature milling condition (30 kV, 0.26 nA) used for comparison with the corresponding cryogenic condition in (i).

The effects of rapid thermal annealing (RTA) temperature on the structural and electrical properties of 10 nm-thick Hf_0.5Zr_0.5O₂ (HZO) thin films were investigated. Structural analyses revealed that the films remained largely amorphous at low annealing temperatures and crystallized above 600 °C, where the ferroelectric orthorhombic phase became dominant. At higher temperatures, the formation of the monoclinic phase was also observed. Electrical characterization demonstrated a strong dependence of ferroelectric behavior on annealing temperature. Films annealed near 600 °C exhibited the most stable ferroelectric domains, strongest polarization switching, and most distinct hysteretic behavior, whereas higher temperatures led to a gradual degradation of the electrical response. These results indicate that an annealing temperature around 600 °C provides the optimum condition for achieving enhanced ferroelectric performance in HZO thin films.

Cryogenic-temperature friction stir processing (CT-FSP) was performed on AA6xxx sheets at 600 RPM and 500 mm/min using in-process liquid N₂ cooling to investigate microstructure, precipitate evolution, and the resulting mechanical response. Multiscale characterization EBSD, SEM/EDS and microhardness tests were conducted. CT-FSP produced a highly refined predominantly equiaxed stir zone (SZ) with average grain sizes of approximately 1.6–1.8 µm at the surface and mid-thickness, and slightly coarser grains (~ 4.4 µm) near the bottom and within the thermomechanically affected zone (TMAZ). Dynamic recrystallization, evidenced by a high fraction of high-angle grain boundaries and low KAM, dominates the SZ. The recrystallization fraction varies laterally and through the thickness due to heterogeneous strain and thermal fields. Second phase particles experience mechanical fragmentation, partial solvus dissolution, and rapid reprecipitation during CT-FSP, yielding a finer and more uniformly dispersed distribution in the upper SZ, while coarser Al–Fe–Si and Mg₂Si particles persist near the bottom/TMAZ. Deep-learning-based image segmentation reveals that the mean equivalent-circle diameters of Al–Fe–Si and Mg₂Si phases decrease from ~ 0.97 µm and 0.80 µm in the as-received sheet to ~ 0.6–0.8 µm locally after CT-FSP, accompanied by reduced nearest-neighbor spacing in the SZ. This localized particles refinement and redistribution, together with extensive DRX, accounts for the combined SZ softening and TMAZ hardening, establishing a clear microstructure-property linkage in cryogenic FSPed AA6xxx sheet.

In this study, urchin-like CuO/Cu₂O mixed-phase nanostructures were synthesized via a simple surfactant-assisted approach, where the surfactant regulated the nucleation and anisotropic growth, leading to a hierarchical morphology with radially arranged nanoneedles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses verified the coexistence of CuO and Cu₂O phases within individual microspheres. High-resolution transmission electron microscopy (HRTEM) revealed well-defined lattice fringes assigned to Cu₂O, while XRD, XPS, SAED, and EDS analyses collectively suggest the coexistence of CuO and Cu₂O phases within the hierarchical microspheres. Energy-dispersive spectroscopy (EDS) mapping and line-scan profiles indicated a gradual compositional variation of copper and oxygen from the core to the surface region. Furthermore, in situ electron-beam irradiation demonstrated structural densification of the urchin-like architecture, providing insight into its structural stability. These results offer fundamental understanding of mixed-phase copper oxide formation and highlight their potential for high-surface-area functional materials.

This paper reviews a recent microstructure control strategy for steels based on intentional chemical heterogeneity, referred to as “chemically heterogeneous steels” or “chemically patterned steels.” This approach introduces controlled chemical inhomogeneity, which has traditionally been avoided, in order to diversify microstructural design and enhance mechanical properties. The strategy involves a three-step process: (i) introducing compositional variations in a multiphase region, (ii) preserving these variations through rapid austenitization, and (iii) controlling microstructural evolution during subsequent cooling. Chemical heterogeneity is introduced via austenite reversion, carbide precipitation, or pearlitic microstructures, enabling precise control of concentration gradients and characteristic length scales. Building on this processing route, the review emphasizes two primary mechanisms for property improvement. First, localized elemental partitioning stabilizes a higher fraction of retained austenite with a broad stability spectrum, inducing a progressive transformation-induced plasticity (TRIP) effect that enhances ductility. Second, the resulting “chemical boundaries” act as physical barriers to dislocation motion and crack propagation, increasing strength and resistance to hydrogen embrittlement. Finally, the paper suggests extending this concept beyond Mn to other alloying elements such as Cr and Ni, as well as its potential application to titanium alloys and implementation in industrial-scale production lines.

Public biological data repositories not only ensure research reproducibility and transparency but also enable new scientific discoveries that extend beyond the scope of original studies. A previously published study on umbelliferone (UMB) demonstrated recovery of synaptic vesicle architecture under scopolamine (SCO)-induced pathological conditions, and the corresponding high-resolution electron microscopy dataset was deposited in the Korea BioData Station (K-BDS, https://kbds.re.kr), a national biological data platform.

In this study, we reanalyzed this open dataset to investigate whether UMB also affects the postsynaptic density (PSD), a previously unexplored structural determinant of synaptic efficacy and plasticity. Using the original high-resolution transmission electron microscopy images, we performed secondary quantitative analyses focusing on PSD length, width, and ultrastructural features across experimental groups. Our reanalysis revealed that UMB treatment significantly increased PSD length and width compared with the SCO-treated group, indicating a structural restoration of impaired postsynaptic architecture. Notably, these PSD-level alterations were not described in the original publication, demonstrating that novel biological insights can be derived from existing data through purposeful reuse.

Collectively, this study underscores the value of K-BDS as a national biological data platform that facilitates secondary discovery and advances data-driven neuroscience research without additional animal experimentation.